Module: ActiveRecord::Inheritance::ClassMethods

Defined in:
activerecord/lib/active_record/inheritance.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#abstract_classObject

Set this to true if this is an abstract class (see abstract_class?). If you are using inheritance with Active Record and don't want a class to be considered as part of the STI hierarchy, you must set this to true. ApplicationRecord, for example, is generated as an abstract class.

Consider the following default behaviour:

Shape = Class.new(ActiveRecord::Base)
Polygon = Class.new(Shape)
Square = Class.new(Polygon)

Shape.table_name   # => "shapes"
Polygon.table_name # => "shapes"
Square.table_name  # => "shapes"
Shape.create!      # => #<Shape id: 1, type: nil>
Polygon.create!    # => #<Polygon id: 2, type: "Polygon">
Square.create!     # => #<Square id: 3, type: "Square">

However, when using abstract_class, Shape is omitted from the hierarchy:

class Shape < ActiveRecord::Base
  self.abstract_class = true
end
Polygon = Class.new(Shape)
Square = Class.new(Polygon)

Shape.table_name   # => nil
Polygon.table_name # => "polygons"
Square.table_name  # => "polygons"
Shape.create!      # => NotImplementedError: Shape is an abstract class and cannot be instantiated.
Polygon.create!    # => #<Polygon id: 1, type: nil>
Square.create!     # => #<Square id: 2, type: "Square">

Note that in the above example, to disallow the creation of a plain Polygon, you should use validates :type, presence: true, instead of setting it as an abstract class. This way, Polygon will stay in the hierarchy, and Active Record will continue to correctly derive the table name.


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# File 'activerecord/lib/active_record/inheritance.rb', line 158

def abstract_class
  @abstract_class
end

Instance Method Details

#abstract_class?Boolean

Returns whether this class is an abstract class or not.


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# File 'activerecord/lib/active_record/inheritance.rb', line 161

def abstract_class?
  defined?(@abstract_class) && @abstract_class == true
end

#base_classObject

Returns the class descending directly from ActiveRecord::Base, or an abstract class, if any, in the inheritance hierarchy.

If A extends ActiveRecord::Base, A.base_class will return A. If B descends from A through some arbitrarily deep hierarchy, B.base_class will return A.

If B < A and C < B and if A is an abstract_class then both B.base_class and C.base_class would return B as the answer since A is an abstract_class.


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# File 'activerecord/lib/active_record/inheritance.rb', line 99

def base_class
  unless self < Base
    raise ActiveRecordError, "#{name} doesn't belong in a hierarchy descending from ActiveRecord"
  end

  if superclass == Base || superclass.abstract_class?
    self
  else
    superclass.base_class
  end
end

#base_class?Boolean

Returns whether the class is a base class. See #base_class for more information.


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# File 'activerecord/lib/active_record/inheritance.rb', line 113

def base_class?
  base_class == self
end

#descends_from_active_record?Boolean

Returns true if this does not need STI type condition. Returns false if STI type condition needs to be applied.


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# File 'activerecord/lib/active_record/inheritance.rb', line 76

def descends_from_active_record?
  if self == Base
    false
  elsif superclass.abstract_class?
    superclass.descends_from_active_record?
  else
    superclass == Base || !columns_hash.include?(inheritance_column)
  end
end

#finder_needs_type_condition?Boolean

:nodoc:


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# File 'activerecord/lib/active_record/inheritance.rb', line 86

def finder_needs_type_condition? #:nodoc:
  # This is like this because benchmarking justifies the strange :false stuff
  :true == (@finder_needs_type_condition ||= descends_from_active_record? ? :false : :true)
end

#inherited(subclass) ⇒ Object


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# File 'activerecord/lib/active_record/inheritance.rb', line 199

def inherited(subclass)
  subclass.instance_variable_set(:@_type_candidates_cache, Concurrent::Map.new)
  super
end

#new(attributes = nil, &block) ⇒ Object

Determines if one of the attributes passed in is the inheritance column, and if the inheritance column is attr accessible, it initializes an instance of the given subclass instead of the base class.


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# File 'activerecord/lib/active_record/inheritance.rb', line 50

def new(attributes = nil, &block)
  if abstract_class? || self == Base
    raise NotImplementedError, "#{self} is an abstract class and cannot be instantiated."
  end

  if has_attribute?(inheritance_column)
    subclass = subclass_from_attributes(attributes)

    if subclass.nil? && scope_attributes = current_scope&.scope_for_create
      subclass = subclass_from_attributes(scope_attributes)
    end

    if subclass.nil? && base_class?
      subclass = subclass_from_attributes(column_defaults)
    end
  end

  if subclass && subclass != self
    subclass.new(attributes, &block)
  else
    super
  end
end

#polymorphic_class_for(name) ⇒ Object

Returns the class for the provided name.

It is used to find the class correspondent to the value stored in the polymorphic type column.


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# File 'activerecord/lib/active_record/inheritance.rb', line 195

def polymorphic_class_for(name)
  name.constantize
end

#polymorphic_nameObject

Returns the value to be stored in the polymorphic type column for Polymorphic Associations.


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# File 'activerecord/lib/active_record/inheritance.rb', line 188

def polymorphic_name
  base_class.name
end

#sti_class_for(type_name) ⇒ Object

Returns the class for the provided type_name.

It is used to find the class correspondent to the value stored in the inheritance column.


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# File 'activerecord/lib/active_record/inheritance.rb', line 173

def sti_class_for(type_name)
  if store_full_sti_class
    ActiveSupport::Dependencies.constantize(type_name)
  else
    compute_type(type_name)
  end
rescue NameError
  raise SubclassNotFound,
    "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " \
    "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " \
    "Please rename this column if you didn't intend it to be used for storing the inheritance class " \
    "or overwrite #{name}.inheritance_column to use another column for that information."
end

#sti_nameObject

Returns the value to be stored in the inheritance column for STI.


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# File 'activerecord/lib/active_record/inheritance.rb', line 166

def sti_name
  store_full_sti_class ? name : name.demodulize
end